Pharmacology
The therapeutic pharmacological properties of zopiclone include hypnotic, anxiolytic, anticonvulsant and myorelaxant properties. Both zopiclone and benzodiazepines act indiscriminately at the benzodiazepine binding site on α1, α2, α3 and α5 GABAA containing receptors as full agonists causing an enhancement of the actions of GABA to produce the therapeutic and adverse effects of zopiclone. The metabolite of zopiclone called desmethylzopiclone is also pharmacologically active although it has predominately anxiolytic properties. Like benzodiazepines zopiclone and its active metabolite desmethylzopiclone also inhibit N-methyl-D-aspartate (NMDA) receptors and nicotinic acetylcholine (nAChRs) receptors which might play a role in the addictive properties of these drugs. One study however, found some slight selectivity for zopiclone on α1 and α5 subunits. Although it is regarded as being unselective in its binding to α1, α2, α3 and α5 GABAA benzodiazepine receptor complexes. Desmethylzopiclone has been found to have partial agonist properties unlike the parent drug zopiclone which is a full agonist. The mechanism of action of zopiclone is similar to benzodiazepines, with similar effects on locomotor activity and on dopamine and serotonin turnover. A meta-analysis of randomised controlled clinical trials which compared benzodiazepines to zopiclone or other Z Drugs such as zolpidem, zaleplon has found that there are few clear and consistent differences between zopiclone and the benzodiazepines in terms of sleep onset latency, total sleep duration, number of awakenings, quality of sleep, adverse events, tolerance, rebound insomnia and daytime alertness. Zopiclone is in the cyclopyrrolone family of drugs. Other cyclopyrrolone drugs include suriclone. Zopiclone although molecularly different from benzodiazepines, shares an almost identical pharmacological profile as benzodiazepines including anxiolytic properties. Its mechanism of action is via binding to the benzodiazepine site and acting as a full agonist which in turn positively modulates benzodiazepine sensitive GABAA receptors and enhances GABA binding at the GABAA receptors to produce zopiclone's pharmacological properties. In addition to zopiclone's benzodiazepine pharmacological properties it also has some barbiturate like properties.
In EEG studies, zopiclone significantly increases the energy of the beta frequency band and shows characteristics of high-voltage slow waves, desynchronization of hippocampal theta waves and an increase in the energy of the delta frequency band. Zopiclone increases both stage 2 and slow wave sleep (SWS), while zolpidem, an α1-selective compound, increases only SWS and causes no effect on stage 2 sleep. Zopiclone is less selective to the α1 site and has higher affinity to the α2 site than zaleplon. Zopiclone is therefore very similar pharmacologically to benzodiazepines.
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